1. Field of the Invention
The present invention relates to an exposure meter system for cameras. More specifically, it relates to a technique for use in an exposure meter system that measures brightness in divided areas. The technique makes quick exposure control possible by eliminating the computing operation for obtaining exposure data under specified conditions.
2. Description of Related Art
In the conventional art, a camera is provided with an exposure meter system to measure the level of illumination of the subject so that suitable exposure can be accomplished. Based on the illumination value obtained by means of such a light metering system, the processing circuits in the camera determine the shutter time and lens aperture stop value so that an appropriate amount of exposure can be given to the film.
Heretofore, the metering system was of a type that measures light weighted mainly in the center of the frame. In recent years, however, it has become more prevalent for the illumination to be measured in more than one area of the subject. This type of meter measuring method is generally referred to as divided brightness measurement. In the metering, the subject image is divided into about 5 or more areas, including the center area and two or more peripheral areas. With this measurement, brightness in the center area of the subject and in the peripheral areas are compared with each other to determine the optimum exposure conditions.
In accomplishing divided brightness measuremenn, the greater the number of divisions the higher the probability of obtaining the correct exposure conditions for the main (center) area as well as for the peripheral areas, because in this manner a more detailed distribution of illumination can be obtained for these areas. Therefore, the number of divisions with divided brightness measurement tends to become increasingly greater. In the future, due to improvements in photocells, the number of divisions is expected to range from several tens to several hundreds.
With cameras in which the above-described divided brightness measurement is accomplished, the computing circuits require little processing time if the number of divisions is kept to a minimum. However, if the number of divisions increases to from several tens to several hundreds or more, the process complexity approaches that of so-called image processing.
This requires a very long processing time before the optimum exposure conditions can be obtained. With a camera in which the use of a one chip CPU is necessitated because of space limitations, and in which the CPU has to perform many processes, including the range-finding process, exposure-controlling process and many other processes, not to mention the light-metering operations, a long time is required in order to obtain the above-described optimum exposure conditions, thereby making instantaneous response on the part of the camera impossible.